1. Field of the Invention
The present invention generally relates to an image forming apparatus, such as for use in forming an image on an image bearing member and, more particularly, for use in an image forming apparatus such as a color digital copying machine or a color laser printer, for forming a color image on the image bearing member.
2. Description of the Prior Art
Recently, the use of color in an image forming apparatus such as a copying machine or a laser printer has rapidly advanced. However, for example, in operating color copying machines, many users have experienced the problem that different images formed from the same original image using the same copying machines have different densities. In these conventional image forming apparatuses, the image density changes are influenced by a change or deterioration of the image forming conditions due to different operating environment factors and an elapse of time. Thus, it is important to stabilize the image density changes. In particular, in a color image forming apparatus, since the image density changes influence not only the density reproducibility but also color reproducibility, a stable image density is an indispensable requirement for maintaining color fidelity.
Therefore, in a conventional image forming apparatus, a given allowance margin (i.e., tolerance) is provided for the image forming materials and the image forming process itself, and image stabilization is attained to some extent by maintaining the materials and process variables within this allowable margin. However, the allowable margins that can be provided for the image forming materials and image forming processes are limited in conventional apparatuses. Also, the cycle in which the image density changes is shorter than a maintenance cycle so that an image having a stable image density may not form by only maintaining the material and process within tolerance. Maintenance cycle, as used herein, refers to the time period within which the tolerances or allowable margins for the image forming materials and process can be maintained.